The present invention relates to a plate mounting apparatus in a printing press, which winds, on the circumferential surface of the plate cylinder, a plate having one end gripped by a leading-side plate lockup device provided in the gap formed in the outer circumferential surface of a plate cylinder, and causes a trailing-side plate lockup device in the gap in the outer circumferential surface of the plate cylinder to grip the other end of the plate, thereby mounting the plate on the plate cylinder.
In a general printing press, leading- and trailing-side plate lockup devices each including a plate lockup table and gripper plates pivotally supported by the plate lockup table are provided in a gap formed in the outer circumference surface of the plate cylinder. The leading end of a plate is gripped by the leading-side plate lockup device by the opening and closing operations of the gripper plates, and wound on the circumferential surface of the plate cylinder by rotating the plate cylinder by almost one revolution, and thereafter the gripper plates are opened and closed so that the trailing-side plate lockup device grips the trailing end of the plate, so that the plate is mounted on the plate cylinder.
In the printing operation, an ink and water are supplied to the surface of the mounted plate to form an image, and the image is transferred to paper being transported directly or through a blanket cylinder, thereby printing the image. In this printing operation, when the plate is distortedly mounted, the image is distortedly printed, degrading the quality of the printed matter. Especially, in multicolor printing, the different colors are misregistered to largely degrade the quality of the printed matter. For this reason, at the time of conventional plate making, U-shaped reference pin holes are formed in the leading end of the plate, and the plate is made with reference to these reference pin holes. Simultaneously, reference pins are provided on the plate gripper portion of the leading-side plate lockup device, and the plate is mounted while engaging the reference pin holes of the plate with these reference pins.
In such a conventional plate mounting apparatus, however, the gripper plates of the leading-side plate lockup device are opened, the end portion of the plate is inserted in the plate cylinder, the U-shaped bottom portion of the reference pin hole is brought into contact with the reference pin to position the plate, and the gripper plates are closed. That is, since whether the reference pin hole contacts the reference pin is confirmed according to the sense of the operator, a skilled operator is required. However, variations caused by the degrees of skills of the operators are inevitable, and satisfactory positioning precision cannot always be obtained. When high-precision positioning cannot be performed, a degradation in printing quality is caused.